The present invention relates to a scanning system and method, more particularly to a scanning system and method using a constant velocity scan with a gimbaled reflecting surface.
Scanning sensors are used in the modern military for surveillance and scouting. More particularly, scanning sensors are used to survey a desired field-of-view (hereinafter abbreviated as xe2x80x9cFOVxe2x80x9d) (such as a section of the sky) within a generally broader field-of-regard (hereinafter abbreviated as xe2x80x9cFORxe2x80x9d) (such as the entire sky within sight). A scanning sensor may be mounted on a stationary structure, a light scout vehicle or a ship, for example.
The scanning sensor may be mounted at an elevated position, on a mast, for example, to maximize the available FOR. Changing the scan direction can induce a twisting moment on the mast, which in turn requires a reaction mass to counter the twisting moment, increases the energy requirements and reduces the maximum scanning speed. The twisting moment created by changing the scan direction also requires a stronger, heavier and more expensive mast to reduce the risk of failure.
If the scanning sensor rotates a complete three hundred sixty degrees at either a constant velocity or at an accelerated rate outside the FOV, substantial time is expended outside the FOV. To minimize the time required to scan within the FOV, scanners which reverse their scan direction at the edges of the FOV have been developed. Reversing the scan direction requires the system to rapidly decelerate, stop, reverse direction and accelerate back to the scanning velocity. However, changing direction reduces the maximum FOV which can be scanned by the distances traveled during the deceleration and acceleration periods.
The present invention provides a scanning system and a method that permit scanning a desired FOR at a constant speed without reversing the scan direction. A scanning system utilizing the present invention can scan a desired FOR with constant scan speed using a gimbaled and articulated reflective surface. Articulating the reflective surface minimizes or eliminates loss of FOR, minimizes or eliminates the need for a reaction mass to counter an excessive twisting moment on the mast, and reduces power consumption because there is no need to decelerate, reverse direction, and accelerate during the scan. Articulating the reflective surface, rather than reversing the scanning direction, also simplifies the system and is expected to lead to increased durability of the system.
In accordance with one aspect of the invention, a system for scanning a field-of-regard includes means for sensing an image, and means for directing an image from the field-of-regard to the means for sensing. The means for directing includes a reflecting surface rotatable about two generally parallel axes.
In accordance with one or more embodiments of the invention, the parallel axes include a central axis and an adjustment axis spaced from the central axis and rotatable about the central axis; the means for sensing includes a sensor package; the reflecting surface is a mirror; the reflecting surface is rotatable about an elevation axis transverse to the adjustment axis; the elevation axis is perpendicular to the adjustment axis; the reflecting surface is rotatable about a flip axis perpendicular to the central axis; and/or the central axis is vertical.
In accordance with one embodiment of the invention, the system may further include a housing having a turret portion rotatable about the central axis and a sight portion mounted to the turret portion and rotatable relative to the turret portion; the reflecting surface mounted on a gimbal within the sight portion; the gimbal including portions that are independently rotatable about the elevation axis and the adjustment axis; and/or the sight portion being rotatable about a flip axis relative to the turret portion.
In accordance with another aspect of the invention, a combination includes a vehicle having a mast and a scanning system having a sensor package, and a mirror rotatable about generally parallel axes to direct an image from a field-of-regard to the sensor package.
In accordance with one or more embodiments of the invention, one of the axes of rotation is substantially aligned with the longitudinal axis of the mast; and/or the other of the axes of rotation is offset from the longitudinal axis of the mast.
In accordance with yet another aspect of the invention, a method for scanning a field-of-regard includes rotating a reflecting surface about two generally parallel axes to direct an image from the field-of-regard to a sensor package for sensing the image.
In accordance with one or more embodiments of the invention, rotating includes rotating about a vertical axis; rotating includes rotating about a central axis and rotating about a generally parallel adjustment axis; rotating about the central axis includes substantially continuously rotating; rotating about the central axis includes rotating at a substantially constant speed; rotating includes rotating about the adjustment axis and rotating at a speed relative to the rotation about the central axis to direct images from a one hundred eighty degree field-of-view to the sensor package; rotating further includes rotating about an elevation axis that is perpendicular to the adjustment axis to provide elevational adjustments; rotating includes indexing the mirror by incrementally rotating the mirror about the elevation axis until the entire field-of-regard has been scanned; rotating includes rotating about the central axis at a rate of sixty degrees per second; rotating includes rotating about the adjustment axis at a rate of about six degrees per second for at least a portion of each revolution about the central axis; rotating includes rotating about the adjustment axis through a range of about fifteen degrees; and/or rotating includes rotating about the adjustment axis at a rate of about thirty degrees per second.
The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this embodiment being indicative, however, of but one of the various ways in which the principles of the invention may be employed.